As the Iraqi led offensive bears down on the major city of Mosul, Daesh is desperately trying to slow the advance, with booby traps, suicide missions, and blowing up a sulfur plant, igniting a toxic blaze.

The UN says there are reports that ISIS has massacred dozens of people near Mosul. And CNN correspondents on the ground say for the first time ever ISIS is facing the resistance inside the city.

This is Gayyara West, America’s largest forward position in Iraq, at the forefront of the battle for Mosul. From the moment you get a call, you can be mobile in this and out firing out on to an enemy position within two minutes?

Lieutenant Keegan Aldridge shows us to the latest generation of precision artillery.

“We are the furthest reaching artillery system on the battle field, highly accurate, highly precise because our system minimizes the collateral damage because there are a lot of urban targets we are prosecuting,” said Lieutenant Aldridge.

This sprawling facility was a base during the U.S.-led occupation of Iraq, some of the blast walls are from those days. When ISIS was finally driven out in August, they destroyed the runway, mounds of earth hid bombs and buildings were booby trapped. Now, the runway is cleared and hundreds of troops are based here, some sleep in tents, others in bunkers.

“And I see everyone has their gas masks…”

“And we have needed them the last couple of days.” That’s because of noxious smoke from a fire set by ISIS at a nearby sulfur plant, which casts a dense pall over a huge area.

Inside the joint operations center commanders closely watch drone feeds that we cannot film. Right now a group of ISIS fighters is the target. Cheers erupt as their convoy is hit.

“The fire support that we have been providing for this operation has been impressive. Since Mosul liberation took off we have dropped over 1700 munitions,” said Major Christopher Parker, Coalition Spokesperson.

However, if all goes according to plan, the operation will have to change.

“The civilian population does complicate the situation and avoiding civilian casualties is a very high priority for the coalition. So we will change the way that we look at our targeting,” said Major Parker.

ISIS has long shown that it’s a determined cunning enemy.

“And the enemy always has a vote.” Major Parker responded saying, “I believe from what I have seen from the Iraqi and Peshmerga with the cooperation and level of support the coalition is providing, I believe that our vote will outweigh their vote.”